Xantia Brakes

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handyman
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Xantia Brakes

Post by handyman »

My Xantia Activa has developed a strange braking phenomena and I wonder if anybody else has had a similar problem and found a solution.
The symptoms are thus:
On applying the footbrake, there feels like no braking effect until you press much harder on the pedal with the consequent neck stretching phenomena as the brake bite hard and stop the car.
A recent check of the brakes, prior to this problem showed worn front discs, one had a step in the centre of the swept area, with uneven wear to the pads. The handbrake cables were replaced about a year ago and work effectively without binding. There seems to be a crack radially on one of the discs.
The rear discs show even wear and the pads are near their worn state.
I have a new accumulator sphere to fit as the pump is on more frequently than it should be.
Could my problem be lack of pressure in the accumulator valve, therefore affecting brake performance?
Are the worn, cracked discs likely to be the cause?
Should I be looking elsewhere for the cause, ie dozer valve? Car has done 133K miles.
My Xantia estate has smooth progressive brakes by comparison. Both cars have fully operational ABS. Any help and advice greatly appreciated.
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Post by Peter.N. »

Sounds like air in the system, try bleeding the front brakes.
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Post by Mandrake »

I have a less severe example of what could be the same problem, that I have been chasing down ever since I got my Xantia. When I first got it the brakes were very poor, (compared to my Dad's Xantia) but I was sure it wouldn't be too much wrong to fix it. (Ha! [}:)])
Things I've done:
* Brake pedal spring removed
* New front and rear pads
* Chamfered edges of pads
* New accumulator sphere
* Replaced faulty rear hydractive centre sphere (affects brakes too)
* Checked front and rear brake pistons and calipers are free
* Bled front and rear brakes
Things not done:
* Anti-sink sphere. (Not tested yet, waiting for pressure tester rig)
Each thing has made a worthwhile improvement, and the brakes have gone from hopeless to fairly good, but they STILL lack an initial sensitive touch that the brakes on my Dad's car have.
When first setting off in the morning light pressure on the pedal has little effect, and the brakes dont start to "bite" until you press fairly hard. If I do 4 or 5 vigorous applications of the brakes on a country road, suddenly the brakes come alive - sensitive to light presses on the pedal and powerful with hard pressure on the pedal, easily able to trigger the ABS on a dry road.
The brakes will then be nice and sensitive for at least a few hours, usually the rest of the day. Then a day or two later they are back to being insensitive for light touches again.
The front discs are reasonably worn - there is a ridge on both edges of the discs that show the surfaces have worn down about 1mm, so before chamfering the edges of the pads, the edges of the pads were definately touching on the ridges first before the main area.
Chamfering has made a big improvement, but hasn't completely solved the problem. The active area of the disc doesn't seem to have any ripples or ridges in it.
Compared to how they initially were (where even emergency stops were hopeless, and couldn't trigger ABS) the hard/emergency braking performance is always good now, and they are also fairly progressive, it's just that they lack sensitivity for light braking after a period of inactivity.
I'm at a bit of a loss what to try next, however they are now performing satisfactorily, so I'll probably leave them for now..
Regards,
Simon
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Post by handyman »

Hi Simon, the effects you have described are exactly the same that my Xantia suffers. I do not use the car much as my wife drives it more regularly, it was only when I went to buy new tyres for it that I noticed the chronic brake performance. It has got progressively worse as my wife now feels the brake performance is not as good as it used to be.
I am mystified as to how air could have entered the system as none of the lines have been disturbed nor fluid level allowed to drop that low!
I will be changing pads and discs today, and will bleed off front brakes to see if it has an effect.
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Post by RichardW »

It's not air, it's nitrogen, and has come from a leaking sphere. Trouble is, there's an awful lot of volume to go at before the sphere gets flat enough to work out which one it is!
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Post by MW »

I had the same thing earlier this year after my garage replaced one of my front calipers and fitted new brake pads (on both sides, obviously). The new pads seemed to take ages to bed in, and I had the same sensation as you - a very poor 'bite' for the first half second or so, then the brakes came in hard so that they practically had to scrape me off the windscreen at every road junction.
I mentioned the problem at my regular service, about a month later, and although they stripped the system down they couldn't find it. Then in the middle of a long motorway trip, it suddenly corrected itself and I was back to normal. Never figured out what caused it.
BTW, if it's any consolation, I found that my brakes DID do the business on emergency stops, even while they were feeling 'soft'. I had a Ferrari cut me up viciously on the M25 and then immediately slam his anchors on hard, and the only that stopped me from shoving his engine up his plasticated @rse was my set of 'soft' brakes. Phew.
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Post by wrinklet1 »

Are your spheres ok, the gass from the sphere can leak over a time into the fluid and build up in the pipes and system. Bleed the brakes, but us a long tube so you can bleed the back into the lhm tank. Put the car in high position before you start bleeding the system.
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Post by ItDontGo »

Jesus dont drive with cracked brakes :-!
You know the stress at a crack tip in an elastic material is infinite. It is only because a material behaves plastically beyond its yield stress that the stress isn't actually infinite in a real material. But regardless there is sufficient stress in a loaded cracked structure to cause it to fail so long as enough energy is supplied. Everytime you brake you will provide the crack with more energy to propagate. Eventually there is going to be a nasty failure.
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Post by Mandrake »

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by MW</i>

I had the same thing earlier this year after my garage replaced one of my front calipers and fitted new brake pads (on both sides, obviously). The new pads seemed to take ages to bed in, and I had the same sensation as you - a very poor 'bite' for the first half second or so, then the brakes came in hard so that they practically had to scrape me off the windscreen at every road junction.
I mentioned the problem at my regular service, about a month later, and although they stripped the system down they couldn't find it. Then in the middle of a long motorway trip, it suddenly corrected itself and I was back to normal. Never figured out what caused it.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Most likely it was the pads riding on the lip at the edge of the disc - my new pads were doing that too, until I took them out and chamfered the edges slightly.
(Something which Dad had told me to do from day one, but I ignored his suggestion at first [;)])
When the disc wears there is usually no wear at the edges, causing a small ridge at each edge, and a new set of pads will usually touch this edge before the main swept area - thus poor braking until you press hard and/or the edge of the pad wears down.
Chamfering the two main edges of the pad speeds this process up to almost immediately being bed in (as long as the swept area is nice and flat) also if you chamfer the small leading and trailing edges then it stops the breaks creaking and groaning when releasing under strain. (EG on an Automatic)
On mine the chamfering immediately fixed the hard braking performance, which was also very poor before.
I suspect the only explanation for the lack of initial sensitivity for light braking is that my discs swept area is slightly non flat, perhaps a slight ridge that is hardly noticable which holds the main pad area away from the disc for light braking.
As soon as you press hard the pad material at that high spot on the disc probably compresses slightly allowing the full pad area to contact and WHAM, strong braking. After doing this a few times a combination of heat and pressure probably causes the pad to hold this new deformed shape for a while - thus good light sensitivity again.
Then after a few hours and the pads cooling down they probably expand back to their flat shape again, and the problem returns.
The only 100% answer would be new discs in that case, (or perhaps machining the old ones) but after a while the pads will probably eventually bed in...
But as a quick first try - pulling out the pads and checking the edges for signs of contact with the lip on the disc and chamfering the edges with a rasp may be all thats needed to get them working well again, provided the swept areas have worn flat.
Regards,
Simon
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Post by Mandrake »

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by ItDontGo</i>

Jesus dont drive with cracked brakes :-!
You know the stress at a crack tip in an elastic material is infinite. It is only because a material behaves plastically beyond its yield stress that the stress isn't actually infinite in a real material. But regardless there is sufficient stress in a loaded cracked structure to cause it to fail so long as enough energy is supplied. Everytime you brake you will provide the crack with more energy to propagate. Eventually there is going to be a nasty failure.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Yikes,
I didnt notice the original poster mentioned cracked discs.... get that replaced immediately! Given the other symptoms (a step in the swept area) and the discussion about it in this thread it seems that two new discs would be needed handyman.
Regards,
Simon
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Post by handyman »

Do Not Panic! The disc was not cracked, it was just a discolouration on the disc surface. The discs and pads have been changed due to the bad wear pattern, i.e. ridges and steps, oh, and being on the wear limit.
I am still intrigued by the nitrogen gas in the system theory. Which sphere do I start with? The ride is as I expect from an Activa, but I have long suspected that the accumulator sphere required changing due to the pump working long hours. The warning light is slow to extinguish on start up and I suppose the poor braking performance could point in that direction. Anybody got a better idea?
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Post by jeremy »

Strangely enough a flat accumulator sphere will make the warning light go out very quickly but I agree a weak one will take longer to charge due to the greater volume of LHM required.
How many spheres on a Activa - 10 is it - all deflating over say 5 years - its a lot of gas for a system that holds say 1 gallon of LHM, 3/4 of which is in a tank.
You could try testing the accumulator by getting the car to normal height and letting it run for a couple of minutes, turn off the engine and sit in the boot. The car should sink and after 30 seconds rise again. It may even do it twice if you are lucky. If it just sinks the accumulator is flat. I think this works on an Activa - but I'm sure Simon will correct me if I'm wrong.
Jeremy
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Post by Jay Farnsworth »

Hi all, ('97 Xantia SX 1.9TD 71K)
I have exactly the same problems you all seem to be mentioning. It didn't start until I changed the discs (and the pads as well), then, as you have all discribed, lots of soft feeling brake, until all of a sudden loads of force and really good braking.
I did notice when I got the tires changed that there is a very pronounced lip on the outer edge of the pad and the inner edge of the disc. This got me scratching my head abit as I double, triple, and quadruple check to make sure I got the correct discs and pads, whilst also noting that there is no way of adjusting the caliper to hub assembly to make the pad fit on the disc better.
Is this lip normal of all xantia brakes? Is it likely that this will solve me weird braking problem? Im seriously concerned as Im lending the car to my uncle for a month and I dont want him to be put off all of a sudden and crash (it can be pretty unnerving when it happens at roundabouts braking from 70).
I changed all five spheres (they needed doing) and it made no difference. The ride is good, there is no evidence of binding, and there are no apparent leeks in the hydro system.
Much regards and thanks in advance to any responses :-)
Jay :-)
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Post by Jay Farnsworth »

Hi again,
After doing some more reading, I also have similar problems to others in another way to the lip. I am also experiencing the squishy, shh, shh sound when I pump the brakes. I guess i will try the full brake bleeding option, although, all the haynes manual (or was it on the andy spares forum) says is to raise and lower the suspension (citrobics) and the system should self bleed through the resivoir. I take it that this is not the complete way of bleeding, any tips before I attempt to look for the bleed nipples? (I have taken note of using a ring spanner and plenty of pre-lub!).
Thanks again Jay :-)
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Post by Jay Farnsworth »

PS Sorry for the change in the start of my first post and the signiture on my second. To clarify, I have a Xantia LX (forgot LX not SX) 1.9TD '97, which is now on 71K, it was on 57K when I wrote the signiture!
Apologies!
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